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Forest Tent Caterpillars Abundant in Saskatoon Again This Year

For immediate release: May 24, 2018 - 8:00am

Forest tent caterpillars, cankerworms, and leafrollers are an annual issue for Saskatoon’s urban forest.  The trees may experience heavy defoliation; however, unless there are underlying issues, the trees will recover and produce new foliage.

Forest tent caterpillars feed on a large variety of trees, including ash, poplar, and chokecherry.  In some cases, these insects can completely defoliate a tree, but trees will typically recover.  After several years of heavy defoliation, trees can decline.

Typically, outbreaks last three to seven years.  Saskatoon is in its fifth year of an outbreak.

Cankerworms, also known as loopers and inchworms, are found primarily on the leaves of American elm and Manitoba maple trees.  The fall and spring cankerworm species often feed together during June and July.  They can be found hanging from silken threads underneath infested trees and can be a nuisance.

Leafrollers feed while concealed within leaves that are rolled or tied together with silk webbing.  Ash trees are their preference, but they also attack other tree species.  The larvae will feed in mid- to late-June, but the leaves will remain rolled throughout the summer.

Tree banding can be used to control cankerworms; however, it is not effective against leafrollers and forest tent caterpillars.  The best time to place bands on trees is from September to May to help prevent the wingless adult female cankerworm moths from climbing host trees to lay their eggs.  It is important to remove the bands at the beginning of June because the bands can collect moisture and cause the trunk to rot.  Unlike the adult female cankerworm, the female leafrollers and forest tent caterpillars have wings and will fly from tree to tree to lay their eggs.

The City does not control forest tent caterpillars, cankerworms, or leafrollers as they typically do not impact the health of the trees they attack.  Home owners interested in controlling them on their own trees should consult their local garden centre for advice.  

For more information on tree pests and diseases, please visit